Virus and Bacteria


» Study of virus is called virology.
» Virus was discovered by Russian scientist Ivanovsky in the year 1892. (During the tests of Mosaic disease in tobacco).
» In nature, there are ultra microscopic particle known as viruses.
» It has both the characters of living and non living, so it is a connecting link between living & non living.
» Dr. Stanley first isolated the virus causing mosaic disease in tobacco in the form of crystals.

Characters of virus
1. They became active inside a living cells.
2. Nucleic acids replicate themselves and they reproduce rapidly.
3. They cause disease like bacteria & fungi.

According to parasitic nature, virus is of three types -
1. Plant virus - RNA is present as its nucleic acid.
2. Animal virus - DNA or sometimes RNA is found in it.
3. Bacteriophage -They depend only on bacteria. They kill the bacteria. DNA is found in them.

» In man virus cause disease like mumps, chicken pox, hepatitis, polio, AIDs and Herpes.
» HIV often change its shape due to the presence of an enzyme reverse transcriptase.
Bacteriophages : Bacteriophages are those virus which infect the bacteria.


It was discovered by Antony Von Leeuwenhook of Holland in the year 1683.
» Leeuwenhook is called the father of Bacteriology.
» In the year 1829 Ehrenberg called it bacteria.
» The year 1843-1892 - Robert Koch discovered the bacteria of Tuberculosis diseases.
» The year 1812-1892 - Louis Pasteur discovered the vaccine of Rabies and pasteurization of milk.

On the basis of shape, bacteria is of different types :
1. Bacillus : This is rod-like or cylindrical.
2. Round or Cocus : These are round and the smallest bacteria.
3. Comma shaped or Vibrio : Like the English sign (,) example – Vibrio cholerae etc.
4. Spirillum : Spring or screw shaped.

» Some species of Azotobacter, Azospirillum and Clostridium bacteria live freely in the soil and fix atmospheric nitrogen into the nitrogenous compound.
» The Bacteria capable of converting nitrite to nitrate is nitrosomonas. Anabaena and Nostoc cynobacteria fix atmospheric nitrogen into soil.
» The species of Rhizobium and Bradyrhizobium etc. bacteria live in the roots of the Leguminous plants capable of converting atmospheric nitrogen into its compound.
» Rhizobium are called symbiotic bacteria.
» The harmful substances produced by the microbes are known as Toxins.
» In leather industry separation of hair and fat from leather is done by bacteria This is called tanning of leather.